The overall objectives of the project are to identify and characterize as completely as possible, the antigens and antibodies responsible for the Cercarienhullen Reaktion, and to attempt to define the role of the CHR in the host-parasite relationship. The experimental animals used in the study are baboons, rabbits, and the Kenyan strain of Schistosoma mansoni. The project is a collaborative program between my laboratory at Abilene Christian College in Abilene, Texas and the laboratory of Dr. Raymond T. Damian, Department of Zoology, The University of Georgia, Athens, Georgia. The objectives of the project are being pursued in three ways: 1) Attempted purification and characterization of CHR antigens and antibodies from isolated CHR sheaths. 2) Serological dissection of the CHR by preparation of CHR positive antisera against the various life cycle stages of S. mansoni and its uninfected intermediate host Biomphalaria pfeifferi, followed by selective absorptions of these antisera by the stage specific antigens. 3) Attempted isolation and characterization of CHR antigens in B. pfeifferi. Ultimately it is hoped to test these antigens for their possible role in resistance to infection or as a possible parasite defense mechanism.